The present invention is directed to a device for conveying and piling flat workpieces, especially die-cut blanks, plates or open paperboard boxes. The apparatus includes a conveyor with endless belts acting stepwise and jointly with a vacuum chamber and ejector, which is destined to remove the flat workpieces from the endless belts of the conveyor with a view of piling them up in a specific pile or store.
As a rule in known devices of the prior art, flat workpieces, such as, for instance, plates or sheets of corrugated board originating from a machine processing them, are pile up in one or several stores. From the stores, they are removed for either storage or ultimate transportation toward another destination, for instance toward another machine in charge of accomplishing an additional operation on the sheets of corrugated board.
In practice, a known device for conveying and piling flat workpieces, such as die-cut blanks, plates or open paperboard boxes, comprises a conveyor with endless belts, which are arranged to extend side-by-side and which have an upper surface of the lower drive run of each belt in contact with supports, which are arranged in such a way as to leave between them an adequate space communicating with a vacuum device containing an ejector equipped with a valve which acts on the support of the endless belts, in such a way as to close the free space left between the supports. The ejector is raised and lowered during a dwell in the movement of the belts to cause an ejection of the sheet of corrugated board from the belts into a pile.
U.S. Pat. No. 3,820,779, whose disclosure is incorporated herein by reference thereto, is directed to a device for carrying sheets of corrugated board by means of a conveyor equipped with several conveyor belts appropriately spaced side-by-side in the crosswise direction. These conveyor belts are carried forward stepwise by an appliance having the shape of a Geneva wheel that looks like a Maltese cross, which wheel coacts with a pin on a rotating lever to cause intermittent movement with a slow-down or deceleration followed by a stand-still for each of the conveyor belts during each plate advance cycle. Moreover, it is foreseen to fit on top of the conveyor belts, a vacuum device designed to aspire or to provide a suction to the sheets of corrugated board to draw the sheet against the conveyor belts, and this aspiration is achieved through the space left open between the belts. Furthermore, a lower part or surface of the vacuum device provides a belt support, which is also appropriately spaced so that the space left free between the belts can be kept.
The device of this patent includes a plate ejector designed to remove plates from the belts so as to have them drop into one or several storage devices. These ejectors consist of two arms connected to one another on their lowest part by a strip designed to engage and contact an upper surface of each of the sheets of cardboard which are to be ejected.
The arms are arranged on both conveyor ends are controlled synchronously with the stepwise belt movement. In order to interrupt the aspiration caused by the vacuum device, the two arms are provided with a flap, which is arranged inside the vacuum device. When the aspiration resumes, the flap is removed from the upper side of the belt supports by stopping devices arranged on both arms of the ejectors. When a plate is ejected, the aspiration is interrupted by the gravity controlled flap, which is to close the upper part of the space between the various belt supports.
One of the disadvantages of the execution of this device is that during the ejection of the sheet of cardboard, there always remains a relative displacement between the ejector and the upper surface of the sheet of cardboard. This slight relative displacement is admissible and can be permitted when having rather low operating speeds. However, on presently built machines with very high production speeds reaching 10,000 sheets per hour, a relative displacement between the ejector and each sheet is not allowable. In fact, with these speeds, a relative displacement between the ejector and the plate will cause an irregular piling of the sheets in the storage device, which will cause an erratic subsequent operation on the batch thus made.
To overcome these drawbacks, it would be helpful, as with other devices, to provide a front stop or baffle, of which the leading edge of the sheet comes to standstill; however, this would then cause the plate front edge to knock against this stop. Such a provision of a stop can also cause damage to the front edge, which is not allowable.
Another drawback which is present with this device occurs with the problem of controlling the setting-in of the aspiration. In fact, as may be gathered from the above-mentioned U.S. patent, the aspiration effect will not be cut immediately with the running of the plate ejection so that the plate will remain stuck to the ejectors during a certain period. This sticking to the ejector will prolong the time needed for the sheet to drop into the pile store and possibly cause a collision when there are high production speeds. At any rate, a prolonged dropping time would impair the performance of the device.
In the device described above, the ejectors are controlled by means permanently connected to the means commanding the stepwise action of the conveyor belts. If it is desirable to use several successive piling stores, this construction is a handicap, since, in such a case, it is not possible to arrange two successive conveyor devices of this type. In fact, since the action of the ejector cannot be neutralized, a double-level plate conveyance system will be a required solution and includes a deflector enabling the plates to be directed to one or the other of the conveying and piling devices. Thus, an additional conveyor is necessary. Such a design would be expensive and, besides that, increases the risk of jeopardizing the piling action.